It seems that after ETIAS is implemented, every dual US/EU citizen who wants to avoid using ETIAS on one end and ESTA on the other end would have to use the following passport routine:
Eastbound
- Airline check-in: EU passport
- In case of random CBP control at the gate: US passport
- Entry border control in Europe: EU passport
Westbound
- Airline check-in: US Passport
- Exit border control in Europe: EU Passport
- CBP control in the US: US Passport
A similar arrangement would apply for dual Canadian/EU citizens.
Do you agree?